In industrial apparatuses, such as incinerators, melting furnaces, power boilers, metal melting furnaces, and the like, hot exhaust gases (hereinafter simply referred to as “gases”) that contain dust-like particles, such as soot are generated in connection with combustion reaction, thermal reaction, or the like at the time of its operation. Then, these gases are discharged to the outside. The gases discharged from the industrial apparatuses are sent to a filter-type dust collector or electric dust collector after cooled to a certain degree of temperature, and the dust-like particles are collected and removed by such a dust collector.
When the filter-type dust collectors and the electric dust collectors are compared with each other, the filter-type dust collectors using bag filters are generally considered superior in dust collecting performance for collecting dust-like particles being dispersed in gases. When temperatures of the gases are high, however, the electric dust collectors are used to collect and remove the dust-like particles with electrostatic forces (collecting ability) since the bag filters cannot be used.
As an above-described electric dust collector, as shown in FIG. 8, there is an electric dust collector provided with: a hollow casing 100 at which a gas inlet 102 and a gas outlet 104 are formed, respectively; discharge electrodes 106 and dust collecting electrodes 108 that are arranged in this casing 100, respectively; and a high-voltage power supply (not shown) that is connected to the discharge electrodes 106 and that applies a driving voltage between these discharge electrodes 106 and dust collecting electrodes 108. In this electric dust collector, as shown in FIG. 8, charges are given to dust-like particles contained in a gas G by corona discharge from the discharge electrodes 106 and then the dust-like particles are electrically charged, while flowing the gas G containing the dust-like particles between the discharge electrodes 106 and the dust collecting electrodes 108. Thereby, these dust-like particles are attracted to the dust collecting electrodes 108 with an electrostatic force, and are then adsorbed.
In addition, an electric dust collector described in, for example, Patent document 1 is known. This electric dust collector described in JP 2004-160286 A (herein “Patent Document 1”) is provided with: a first dust collecting portion on an upstream side in a casing in a flow direction of a gas; and a second dust collecting portion on a downstream side of the first dust collecting portion.
Specifically, a plurality of plate-shape dust collecting electrodes are arranged at the first dust collecting portion and a plurality of rod-shape discharge electrodes are disposed between a pair of dust collecting electrodes at a fixed interval over substantially an entire length in a longitudinal direction of the dust collecting electrodes. The second dust collecting portion is also formed to basically have a similar structure to the first dust collecting portion, and has a plurality of dust collecting electrodes and discharge electrodes, respectively. A high-voltage power supply is connected to the plurality of discharge electrodes in the first and second dust collecting portions, respectively.
In the electric dust collector described in Patent Document 1, the dust collecting electrodes each are formed into an elongated mesh plate in the flow direction of the gas, the discharge electrodes each are formed into an elongated rod that extends in a vertical direction substantially perpendicular to the flow direction of the gas, and are supported to oppose front surfaces or back surfaces of the dust collecting electrodes. Accordingly, what is disclosed is that the contact length of the dust collecting electrode and the gas can be made longer in the flow direction of the gas, and corona discharge can be made to act on the gas over the entire length of the dust collecting electrodes, thus enabling improvement in the dust collection efficiency of collecting the dust-like particles in the gas.
Patent Document 1 discloses that the discharge electrodes and the dust collecting electrodes are densely arranged at the second dust collecting portion on the downstream side, as compared with the discharge electrodes and dust collecting electrodes arranged at the first dust collecting portion on the upstream side. Therefore, even when a gas with a low concentration of dust-like particles is collected, the dust-like particles that fail to be collected at the first dust collecting portion on the upstream side can be collected efficiently at the second dust collecting portion on the downstream side.
It should be noted that, however, when the plurality of dust collecting portions are arranged as well as making the dust collecting electrodes to be elongated in the flow direction of the gas in order to extend the contact length of the dust collecting electrodes and the gas as described in the electric dust collector described in Patent Document 1, the size of the casing in the flow direction of the gas inevitably becomes longer. This may cause a disadvantage due to an installation space of the collector.
In addition, as described in Patent Document 1, when the discharge electrodes and the dust collecting electrodes are densely arranged at the second dust collecting portion on the downstream side as compared with the discharge electrodes and dust collecting electrodes arranged at the first dust collecting portion on the upstream side in order to efficiently collect the dust-like particles from the gas with the low concentration thereof, the dust collecting performance of the dust collecting portion on the upstream side is inferior to that of the dust collecting portion on the downstream side. Therefore, when a gas with a high concentration of dust-like particles is collected, it becomes difficult to keep an appropriate load balance between the dust collecting portion on the upstream side and the dust collecting portion on the downstream side. This may cause a problem that a dust collection efficiency of the collector is degraded.
In view of the above circumstances, an object of the present invention is to provide an electric dust collector that can efficiently improve the dust collecting performance of collecting dust-like particles contained in a gas, while the increase in size of the collector is being suppressed.